This invention relates to hydrocracking and more particularly to the hydrocracking of high boiling hydrocarbon materials to provide valuable lower boiling materials.
High boiling hydrocarbon materials derived from petroleum, coal or tar sand sources, usually petroleum residuum or solvent refined coal, are typically hydrocracked in ebullated (expanded) bed or fixed bed catalytic reactors in order to produce more valuable lower boiling materials such as transportation fuels or lubricating oils. In order to obtain a desired degree of hydrogenation for hydrocracking and hydrotreating, there are typically several reactors in series. As an example, see U.S. Pat. No. 4,411,768. In these systems, the hydrogen partial pressure declines due to the consumption of hydrogen and the production of light hydrocarbon vapors from the cracking of the heavier liquid fractions and the concentration of lighter and typically more paraffinic liquid components increases with increasing residuum conversion. This reduction in hydrogen partial pressure and increase in concentration of lighter more paraffinic constituents results in an increase in sediment formation, limiting the residuum conversion level which can be attained based on either product quality or reactor operability constraints.
The object of the present invention is to reduce the sediment formation and increase the conversion levels for a high boiling hydrocarbon feedstock in a catalyst bed hydrogenation process with a plurality of reactors in series. The invention involves the introduction of an interstage feed between the series of reactors comprising an aromatic solvent and/or a portion of the high boiling hydrocarbon feedstock.